There has been proposed a technique to induce an electric field in an electric-field transmission medium such as a human body, and use the electric-field thus induced to perform a data communication.
FIG. 13 is a schematic view for explaining a communication system which performs an electric-field communication using a human body as an electric-field transmission medium. The communication system shown in FIG. 13 is a communication system which performs a communication by utilizing an electric field induced in a user 401 between a transmitting device 201 and a receiving device 301.
When the transmitting device 201 transmits data to the receiving device 301, the transmitting device 201 induces an electric field Ec in the user 401 by a signal electrode 201A. The receiving device 301 receives data by detecting an electric field Ef induced in the user 401.
However, even though the electric field Ec is induced in the user 401, there still exist an electric field Eb directed back to a ground electrode 201B from the user 401, and an electric field Ee escaping to the ground. Thus, the electric field Ef reaching the receiving device 301 is the difference between the electric field Ec induced in the user 401 and the electric fields Eb and Ee. There also exists an electric field Ea directly inputted to the ground electrode 201B from the signal electrode 201A.
In addition, if the electric-field communication terminal is miniaturized and thus becomes easily portable, a stress is applied to a case of the electric-field communication terminal, causing a problem of a reduction in the electric field Ec induced in the user 401. This is because the stress: brings a mounted component into contact with the electrode arranged inside the case, so that the electric field Ec induced in the user 401 is cancelled; or reduces the distance between the signal electrode 201A and the ground electrode 201B, so that the electric field Ea is increased.
Moreover, when the user 401 touches the signal electrode 201A and the ground electrode 201B simultaneously, the electric field Eb directed back to the ground electrode 201B from the user 401 increases, which in turn reduces the electric field Ef to be detected by the receiving device 301. Consequently, a problem of deterioration in the communication quality occurs.